Left with no choice but to turn to Ra’s to revive a dying Thea, Oliver jets to Nanda Parbat to bring her back to life via the Lazarus Pit. By doing so, he must keep his end of the deal, trading in his former life as Oliver and the Arrow to become Al Sah-him, the rightful heir to the demon.

But… before Oliver says goodbye, unlikely circumstances (ahem, Ra’s) bring him and Felicity together for an evening of passionate love-making and Felicity’s long-awaited “I love you.” Soon after though, Felicity poisons Oliver in a last-ditch effort to break him out of Ra’s’ impenetrable fortress. Her attempt, though commendable, is all for naught. “I love you all the more for it,” Oliver tells Felicity later, before transforming into Al Sah-him by hour's end.

Arrow executive producer Marc Guggenheim breaks down the biggest moments from the episode – including why it was time for Oliver and Felicity to go to the next level.

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1. Team Arrow is forced to pick up the pieces in Starling – again

The next episode, titled “Al Sah-him,” focuses on Oliver’s rigorous transformation into Al Sah-him as well as the challenges the remaining members of Team Arrow face without their captain yet again. “That’s the emotional currency of 3x21,” Guggenheim said. “The character journey of 3x21 is how the hell Team Arrow moves forward without Oliver.”

Oliver staying in Nanda Parbat may seem similar to the time he “died,” Guggenheim assures it’s not the same. “They thought he was dead [then] and in many ways that was easier. Knowing that he’s out there and alive and a member of the League of Assassins, that’s a whole lot harder,” he said, adding that the next episode “is one of our most emotional.”It’s a villain-of-the-week episode; it “just so happens that the villain of the week is Oliver.”

That stirs up emotions for Diggle and Felicity, who find solace in Laurel as they become a “real trinity” moving forward. “They’re processing things in different ways,” Guggenheim said. “Laurel is throwing herself into her work saving the city. Felicity is struggling with heartbreak and grief – she really goes through the seven stages of grief with Oliver.”

But something will happen to Diggle “that really upends Diggle’s world – it’s certainly vis-à-vis Oliver,” he hinted. “That’s something that will have repercussions for the remainder of the season.” At least he’ll have his wife Lyla for moral support. “Right now her biggest responsibility is being supportive of Diggle because Diggle’s going through some very difficult times.”

Olicity fans, this was the episode you’ve been waiting for! But what happens to the couple now that Oliver is aligned with the enemy? Considering his current situation, the answer isn’t abundantly clear. One thing that is clear? The writers had plotted this key Oliver/Felicity moment for a while.

“There was a strong desire to have Oliver and Felicity sleep together before the events of the season finale,” Guggenheim explained when ETonline posed the question. “We knew episode 3x20 was the episode to do it in.”

A lot of discussion went into the appropriate setting for Oliver and Felicity’s love scene; Starling City was considered but the writers ultimately settled with “the romance” of Nanda Parbat. “I’m personally fond of the fact that it’s Ra’s who gives [Felicity] the final push,” Guggenheim said.

As we teased, there was a very good reason why Felicity never reciprocated Oliver’s “I love you’s” until tonight. “That was very deliberate,” he added. “We were holding that back this season, the same way we were holding back them sleeping together. We wanted it to be part and parcel for that moment.”

Guggenheim hinted that the final three episodes of the season “spend a lot of time addressing the question of ‘Is there hope for Oliver?’ and certainly ‘Is there hope for Oliver in Felicity’s mind?’” The next two episodes, in particular, have “very specific things to say about that,” he added.

The Thea who came back to life through the Lazarus Pit won’t be the same Thea we once knew, that much is for sure. We saw some of the side effects (i.e. temporary amnesia) in tonight’s episode, but Guggenheim warns, you haven’t seen it all.

“You can expect that there will be more consequences,” he said. “We sort of established very clearly that the Lazarus Pit returns you, but not always in the condition in which you left. There are a lot of stories still to be told with Thea and her recovery.” (She’ll also reunite with Roy to tie up loose ends.)

As far as Thea’s fractured relationship with her father Malcolm goes, by the end of the season, “there’s a nice bit of closure,” Guggenheim teased. “You feel like their story has had a beginning, middle and end. The feelings that Thea has vis-à-vis Malcolm are pretty clearly explicated by the end.”

4. Oliver’s decision to enter the League turns into a play for Maseo’s soul

The next episode addresses Oliver’s struggle with his decision to stick with the League as Ra’s desired. It “answers that question pretty definitively,” Guggenheim said, pointing to the “opening moments” as a key indicator.

As Oliver integrates himself into the League, Maseo’s loyalty may be up for grabs. “His soul is very much in play,” Guggenheim teased. “In thepast and the present, there’s a little bit of a war for Maseo’s soul. We know from the fact that he joined the League of Assassins, how that ended in the past. But how things end in the present and whether or not he can be redeemed is definitely one of the questions we’re building up toward answering.”

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5. Nyssa looms large in final episodes of season

While all this has been happening, Nyssa has been in Starling City, continuing to train Laurel as she figures out her next move. We’ll start to learn more about her feelings and opinions about Oliver replacing her as heir to the demon beginning in the next episode.

“We’ll learn a lot of things about Nyssa, not in terms of backstory, but we’ll learn how she reacts to things and how she’s dealing with life post-[‘The Offer’] and how Oliver joining the League affects her both emotionally and as a practical matter,” Guggenheim hinted. “She looms very large in these final three episodes.” You’ll see Tatsu in the present day and see her reaction to Oliver’s new life.

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6. Ray and Felicity are “truly kiboshed”

If you watched ETonline’s exclusive sneak peek earlier today, this isn’t be a real shock. “They’re pretty well and truly kiboshed,” Guggenheim confirmed. “Romantically, this is where we leave them.” But Ray and the Atom will still be around (“Ray plays a very large role in all the events” in the final two episodes); in fact, Ray and Felicity have another “meaningful exchange” in the penultimate episode.

“I was watching that scene [in episode 22] and I had to remind myself that they broke up,” Guggenheim said. “Regardless of who you ship and people’s feelings about Ray and Felicity, there’s a lot of chemistry between Brandon [Routh] and Emily [Bett Rickards].”

7. Oliver’s League look has a nice nod to his past

This will take some getting used to. Oliver debuted his new League costume at the end of tonight’s episode, and there are some unique elements to his look – the most obvious being the arrowhead necklace.

“Each uniform is slightly different, slightly modified to fit the person [who’s wearing it],” Guggenheim shared with ETonline, adding that the mask was the biggest point of conversation. “We talked a lot about that mask and what it looks like. It’s very detailed – it has Arabic writing on it and it’s a very personal thing. [Costume designer] Maya Mani really had this one in her teeth and just knew exactly what to do.”

It was ultimately down to two masks and the one they went with has a nice nod to the Arrow, Guggenheim revealed: “We liked the one that had a hint of green in it because it was a bit of a nod to Oliver’s former life.”

What surprised you the most? Are you happy Oliver and Felicity finally professed their love? Do you believe Oliver will stay in the League? Tell us your thoughts below and on Twitter by tweeting Philiana Ng at @insidethetube!